1. The Field of the Invention
This invention relates to filaments (or fibers) for brushes. More precisely, this invention relates to novel, improved filaments for oral care brushes and to oral care brushes including the novel improved filaments.
2. Description of the Prior Art
Brushing the teeth is universally recommended as the most effective way to maintain oral hygiene. While there is disagreement as to the most suitable form of brushing, the toothbrush is acknowledged to be the most effective aid in cleaning the teeth. In turn, the cleaning effectiveness of a toothbrush is dependent on such factors as the brushing habits of the user, the frequency, intensity and duration of brushing and the quality of the brush filaments. There is considerable debate in the art relating to the features which provide a toothbrush having maximized cleaning effectiveness. These factors include the material, size, shape, strength and resiliency of the brush filament and the length, width and overall shape and area of the brushing surface. Other features affecting the cleaning effectiveness of a toothbrush include the number of tufts (bundles of individual filaments), the number of rows of tufts and the arrangement of the tufts on the brush head. However there is general agreement in the art that wear is a crucial factor which can dramatically diminish the effectiveness of a toothbrush in maintaining oral hygiene. For example, the art recognizes and acknowledges that diminished effectiveness of a toothbrush by wear can result in increased plaque accumulation and increased risks to periodontium tissue.
The degree of wear of a toothbrush is primarily a function of the properties of the filament and the mechanical force applied to the brush during brushing. The degree of wear can also be accelerated to some extent by abrasive materials normally contained in dentifrices. Brush wear results in tearing, splaying, expansion and fraying of the filaments and a decrease in strength and resiliency of the filaments which is manifested by single filaments deviating from their original direction. Moreover, wear is manifested by a change in the overall shape and size of the brushing surface area and by changes in the texture of the filament. While toothbrush wear varies from use to user, studies indicate that the average toothbrush subject to average use has a useful effective life from about eight to twelve weeks. Thereafter, wear causes sufficient deterioration of the filaments to warrant replacement of the brush in order to assure continued maintenance of effective oral hygiene.
Unfortunately, toothbrushes are not usually replaced regularly and often times are used far beyond their effective useful life. As mentioned, the dental profession has recommended replacement of toothbrushes after about three months of use. However, annual, toothbrush consumption figures indicate that toothbrush user replace their toothbrushes about once a year. The dental profession has made an earnest effort to educate the public about the need to assess the wear of a toothbrush being used to determine if it should be discarded and replaced. However, these efforts have had limited success since the user has the responsibility to remember the condition of a toothbrush which should be discarded and to remember to monitor and continually assess the condition of the toothbrush. Accordingly, a more effective approach is needed to provide reliable means to signal or warn a toothbrush user when a toothbrush has become sufficiently affected by the wear that it should be discarded and replaced.
U.S. Pat. No. 4,802,255 and Pending PCT application Ser. No. 92/04589, both incorporated herein by reference, describe brush filaments, particularly toothbrush filaments which include a colorant which is adapted to provide a color intensity which can change in response to increased use of the filament to provide a signal indicative of filament wear. A line of toothbrushes covered by the claims of these patents has been successfully marketed by Oral-B Laboratories, Redwood City, Calif. under the Indicator.sup.R brand. In the manufacturing methods of these patents, an outer color region is provided by ring dying monofilaments. In a ring dying process, the filament is contacted with a dye for a time sufficient to at least color the outer surface and to also penetrate into a portion of the cross sectional area.
Through a careful investigation of the Indicator.sup.R products we have discovered two previously unknown shortcomings or problems with the product. First, dye penetration is not uniform at different depths along the annular circumference of the bristle. As a result, the darker regions on the outside wear first, while lighter blue persists for a considerable period of time. It would be desirable to have a darker region which is uniform in color density for a fixed depth along the annular circumference of the bristle ring. This would result in a line of clear demarkation of dyed sheath material versus undyed core filament material. The second problem relates to overall dye intensity. During the ring dyeing operation if a high level of dye concentration is used, the resulting bristles are darker; however, the dye material penetrates into the core at a much greater degree. Thus, it is difficult to produce a dark colored, ring dyed material with a thin, dark ring coating.
The following background patents also relate generally to the present invention:
U.S. Pat. No. 2,328,998 to Radford, issued Sep. 7, 1943 discloses an attrition product, e.g., toothbrush filament including a co-mingled abrasive material. FIGS. 3 and 4 disclose a composite filament including a non-abrasive core with a co-mingled abrasive material. FIG. 8 shows a batch-wise apparatus for extruding the filament of FIGS. 3 and 4.
U.S. Pat. No. 3,016,554 to Peterson, issued Jan. 16, 1962 discloses a wire brush filament on to which a plastic coating, e.g., nylon, is extruded as a vibration dampening coating. This bristle is then dip coated with a thin epoxy protective layer. The nylon layer is said to have a general thickness about one half the diameter of the wire core plus or minus 50% (see column 2, lines 67 to 69).
U.S. Pat. No. 3,258,805 to Rossnan, issued Jul. 5, 1966 discloses a wear indicating toothbrush bristle comprised of a nylon filament which is entirely encased within a coating of colored rubber (see column 1, lines 30 to 37). This bristle is said to produce an erasing, instead of grinding, action in cleaning the teeth. Also, it states that the wear on the tips of the bristles gives a visual indication of warning when the brush is ready to be discarded.
U.S. Pat. No. 3,327,339, issued Jun. 27, 1967 and Re. No. 26,688, reissued Oct. 14, 1969 to Lemelson disclose composite plastic filaments formed by extruding different polymers one over the other and each imparting a different useful characteristic to the composite filament (see column 1, lines 11 to 15). The core member is said to be preferably a synthetic textile filament such as nylon. The outer jacket layer is described as a flexible cellular plastic material (see column 2, lines 37 to 41 and Column 4, lines 74 through column 5, line 7). FIGS. 3 and 4 show an element comprising a core made from a more rigid material than the surrounding jacket which is made by simultaneously extruding both the core and jacket as a unitary rod or filament (see column 3, line 74 to column 4, line 20). The jacket is said to comprise the major portion of the filament and is in the order of 0.005 inches to 0.030 inches or greater in outside diameter while the core element or thread is about 0.010 inches in diameter or less (see column 4, lines 70 to 74).
U.S. Pat. No. 3,403,070 to Lewis, issued Sep. 24, 1968, discloses a composite filament. These cellular foam filaments are said to be useful as bristles and mop fibers. The filament comprises an unoriented polyolefin shell and an inner core of polyurethane foam. The shell is described as a coating which has a radius to the annular wall thickness ratio of at least 4 to 1. Furthermore, Applicants believe this coated filament is not an extruded bristle due to the soft, foamy nature of the core material.
U.S. Pat. No. 4,263,691 to Pakarnseree, issued Apr. 28, 1981, discloses a toothbrush bristle comprised of a stiff core made of a hard thermoplastic material such as nylon 6 or high density polyethylene and an outer elastomeric sheath. The sheath is said to be made of a soft thermoplastic such as ethylene vinyl acetate co-polymer, polyethylene, poly-vinyl chloride, or natural or synthetic rubbers. Regarding thicknesses, it is disclosed that if the diameter of the core is d and the outer diameter of the sheath is D, then the ratio d:D can be in the range of 1:1.01 to 1:2.5 (column 2, lines 10 to 13). FIG. 4 illustrates a filament of material produced by continuous extrusion molding of a substance suitable for the core and a substance suitable for the sheath of the bristle. The filament may be made into bristles with the stiff core exposed at the ends or with the ends of the stiff core covered by the sheath (see column 2, lines 14 to 28 and FIG. 7).
U K. patent application, Ser. No. 2,137,080, to Weihrauch, assigned to Coronet-Werk Heinrich Schlerf GmbH discloses plastic bristles or filaments for brushes which also change color in response to wear. The filaments disclosed in the U.K. Application are composite filaments and include a colored core completely surrounded by an outer cover material having a color different from the core color. The cover is injection molded directly onto the core. In the disclosed filaments, the core is a reinforcing element and is relatively hard and stiff to control the rigidity of the filament while the outer cover material is softer than the core material and is more susceptible to wear. In use, the cover material becomes worn in the area of the rounded end of the filament and peels or breaks off to expose the core color to signal that the brush should be discarded.
It is an object of the present invention to produce a composite toothbrush filament containing a colored outer sheath and a different colored inner core material which has a clear line of demarkation at a magnification of about 250X.
It is yet another object of the present invention to provide a wear indicating toothbrush filament with a greater degree of color intensity in the core and/or sheath.
It is another object of the present invention to produce striped wear indicating bristles as an alternative to ring dyed bristles.
It is yet another object of the present invention to provide a more efficient method of producing wear indicating bristles.
Still yet another object of the present invention to provide color-change type, wear indicating bristles with a more desirable color change.
These and other objects will be evident by the following: